The present invention relates generally to bridged carbocyclic compounds. This invention also relates to the use of these compounds, for example, as monomers that can be homopolymerized or copolymerized with other reactive components to make resins within sub-200 nanometer (nm) photoresist compositions.
Photoresists are photosensitive films that are used for the transfer of images to a substrate. In a typical lithography process, a substrate is generally coated with either a positive or negative photoresist coating. The photoresist-coated substrate is then exposed through a photomask to an activating radiation source which transfers the pattern of the photomask onto the photoresist-coated substrate. Depending upon whether the photoresist coating is positive or negative, the radiation source either increases or decreases its solubility in a subsequently applied developer solution. In a positive photoresist coating, the areas masked from the radiation source remain after development while the exposed areas are dissolved away whereas in a negative photoresist coating the opposite occurs. The patterned photoresist image acts as a mask for subsequent substrate patterning processes such as etching, doping, and/or coating with metals, other semiconductor materials, or insulating materials.
Current interest in the semiconductor industry has increased in photoresists that can be photoimaged with short wavelength radiation, i.e., exposure radiation of about 200 nm or less such as 193 nm (ArF laser) or 157 nm (F2 excimer beam laser) wavelengths. Short exposure wavelengths may allow for the formation of smaller features within the semiconductor device. In this connection, a photoresist that can provide well-resolved images after exposure to a 193 nm or 157 nm wavelength radiation source may allow for the formation of relatively smaller (e.g., sub-0.25 μm) features. Smaller device features meet the industry demands for smaller dimension circuit patterns and provide for greater circuit density and enhanced device performance.
Photoresist materials, particularly sub-200 nm materials, are particularly challenging to develop because of the need to balance a variety of different performance characteristics. Photoresist materials should ideally provide high transparency at the exposure wavelength, sufficient resistance to plasma-etching processes, and functional groups that are capable of undergoing sufficient photochemical transformations that change the solubility in developer solutions. Besides these, other important characteristics include, but are not limited to, reasonably simple synthesis procedures, adhesion to the underlying substrate, glass transition temperatures compatible with typical processing temperatures, acceptable shelf storage lifetime, and minimum toxicological risk.
The prior art discloses a variety of monomers that can be polymerized and used as base resins within photoresist compositions for sub-200 nm applications. For the higher end of this range (e.g. 193 nm), cycloaliphatic structures have drawn the most attention. For lower wavelength applications (e.g. 157 nm), the monomers tend to have one or more electron-withdrawing groups such as fluorine or hydroxyl and one or more cyclic structures. It is believed that the combination of the electron-withdrawing groups and the one or more cyclic structures improve the performance of the photoresist composition, particularly transparency.
The preparation of bicyclo[2.2.1]hept-5-ene-2-(1,1,1-trifluoro-2-trifluoromethylpropan-2-ol), also known as NBHFA, and its use in photoresist polymers was first described by H. Ito, et al., “Synthesis and Evaluation of Alicyclic Backbone Polymers for 193 nm Lithography”, American Chemical Society, 1998. Since then it has become an industry benchmark for 157 nm photoresists. The norbornene monomers disclosed therein were synthesized by a Diels-Alder Reaction. One reaction disclosed within the reference is as follows:
The optical density (OD) of the homopolymer (expressed as Absorption at 157 nm divided by the film thickness) was later reported to be 1.7 micrometers−1 (Ito et al, SPIE Proceedings, Vol. 4690 (2002), 18–28).
U.S. Patent Application US2002/0004570 (“Zampini I”) describes photoresist compositions that contain polymerized units of cyclic olefin monomers having one or more pendant cyclic electron-withdrawing groups. The pendant cyclic electron-withdrawing groups disclosed may be N-based, O-based, or S-based.
European published patent application WO 02/21214 (“Zampini II”) discloses base resins within 157 nm photoresist compositions that contain at least one electronegative group that includes aromatic groups such as phenolic moieties. In this connection, Zampini II specifically describes vinyl ether entities that incorporate fluorinated aromatic structures as the electronegative group.
European published patent application WO 02/21213 (“Taylor”) describes resins that are used within photoresist compositions that contain photoacid-labile deblocking groups substituted with one or more electron-withdrawing groups. The electron-withdrawing moieties within the resin are bonded to the blocking group so that the acid-catalyzed blocking and deblocking reactions are relatively unaffected by their presence.
Japanese Application JP 2002/179,731 (Chemical Abstracts 137:54625; “Harada I”) discloses photoresist resins that contain the structure: CO2CR1R2R where R1 and R2=H, F, or a C1-20 alkyl and R=C3-20 cyclic alkyl. In addition, Harada I describes an acrylate resin that contains fluorinated alkyl groups in ester side chains.
U.S. Patent Application 2002/0051936 (“Harada II”) describes an acrylic resin that contains repeating units containing a fluorinated hydrocarbon group, an acid labile group, and an adhesive group. Harada II describes one of the units, preferably the acid labile group, as having at least one alicyclic structure. Harada II also describes acrylic polymers containing the structure —O—C(R1R2)—C(H)(R3)R4, where R1, R2, R3, and R4 are H, F, or an unsubstituted or fluorinated, straight, branched or cyclic alkyl group. Transparencies are reported from 25–45% for 200 nm films measured by transmission spectroscopy.
European Application EP 1 126 322 describes resins for use in a 157 nm photoresist that contain fluorinated ester groups. Transparencies are reported from 40–60% for 300 nm films measured by transmission spectroscopy.
European Application EP 1,103,856 (“Tsutsumi”) describes a fluorine-containing resin that contains polymerized units of an acrylic or methacrylic acid ester wherein the ester moiety comprises a fluorine-containing group. Tsutsumi further describes moieties where the fluorine-containing group has a cyclic structure such as a fluorine-containing benzene ring, a fluorine-containing cyclopentane ring, a fluorine-containing cyclohexane ring, or a fluorine-containing cycloheptane ring. Transparencies are reported from 51–68% for 100 nm films measured by transmission spectroscopy.
US 0059710A1 discloses the following composition useful as a photoresist composition:

wherein Re is a hydrogen atom or an organic group; W2 is a linkage group; Rf is a hydrogen atom or a hydroxyl-protecting group; and Rz is a group containing a fluorine atom, where carbon atoms constituting the ring in the formula may each have a substituent. Additionally, US 0059710A1 discloses in Example 14, the reaction of 5-hydroxybicyclo[2.2.1]-2-heptene and hexafluoroacetone to produce 5-[1,1-bis(trifluoromethyl)-1-hydroxymethyl]oxybicyclo[2.2.1]-2-heptene:

WO 00/67072 discloses the following composition useful as a photoresist

As described in Example 3 of WO 00/67072, the photoresist material was made by reacting sodium hydride, hexafluoroisobutylene epoxide, and 5-norbornene-2-methanol in anhydrous DMF. Sodium hydride is pyrophoric, making this process difficult to commercialize.
Many of the monomers that are known to be useful in a photoresist material must be copolymerized with fluoroolefins or the like to form a useful photoresist material, for example, see the “Binder 2 Preparation Procedure” on page 24 of WO 02/31595 A2 which uses 70 parts TFE in a pressurized vessel when making a copolymer to be used as a photoresist material. The tetrafluoroethylene provides improved transparency to the copolymer; however, the tetrafluoroethylene decreases the etch resistance, and causes poor adhesion, and additionally complicates the reaction to make the photoresist material.
Accordingly, there is a need in the art to provide novel resins polymerized from novel monomers that provide high transparency at sub-200nm wavelengths. These monomers can be used to make homopolymers useful as photoresist materials, if desired. There is also a need in the art for new industrial processes to make fluorine-containing monomers providing improved transparencies.
All references cited herein are incorporated herein by reference in their entirety.